FBI Director James Comey and then-CIA Director John Brennan -- both appointed by President Barack Obama -- issued public warnings over the past two years about a terrorist threat to the United States that demanded a rational response from the president.

Donald Trump has now provided one.

Comey issued a key warning in the House Homeland Security Committee on Oct. 21, 2015.

Rep. Bennie Thompson, the committee's ranking Democrat, asked Comey about an assistant FBI director having informed the committee that -- as Thompson put it -- "the concern in Syria is that we don't have systems in place on the ground to collect the information to vet."

"Databases don't hold the information on these individuals," Thompson said. "Is that still the position of the department?"

"Yes," said Comey, "I think that is the challenge we are talking about, is that we can only query against that which we have collected. And so if someone has never made a ripple in the pond in Syria in a way that would get their identity or their interest reflected in our database, we can query our database until the cows come home but ... there will be nothing show up because we have no record of the person."

Eight months later -- on June 16, 2016 -- Brennan told the Senate Select Committee on Intelligence that the battle against the Islamic State had not diminished its terrorism capabilities.

"Unfortunately," Brennan said, "despite all our progress against ISIL on the battlefield and in the financial realm, our efforts have not reduced the group's terrorism capability and global reach."

"In fact," Brennan said, "as the pressure mounts on ISIL, we judge that it will intensify its global terror campaign to maintain its dominance of the global terrorism agenda."

How would it do this?

"We judge," Brennan said, "that ISIL is training and attempting to deploy operatives for further attacks. ISIL has a large cadre of Western fighters who could potentially serve as operatives for attacks in the West. And the group is probably exploring a variety of means for infiltrating operatives into the West, including refugee flows, smuggling routes and legitimate methods of travel."

Three months after Brennan warned that the Islamic State was likely looking at "refugee flows, smuggling routes, and legitimate methods of travel" to send terrorists West, Comey testified in the House Homeland Security Committee.

"They will not all die on the battlefield in Syria and Iraq," Comey told that committee on Sept. 27, 2016. "There will be a terrorist diaspora sometime in the next two to five years like we've never seen before."

"(W)hen ISIL is reduced to an insurgency and those killers flow out," said Comey, "they will try to come to Western Europe and try to come here to kill innocent people. We have to keep our eye on it and be ready for it."

This was not the first time Comey testified to this.

Back on June 11, 2014, for example, he warned the House Judiciary Committee.

"I see the progeny of al-Qaida, these virulent franchises of al-Qaida, thriving in the poorly governed or ungoverned spaces around the Gulf, in North Africa, around the Mediterranean," Comey testified then. "This remains a huge, diverse and significant threat to us -- through al-Qaida in the Arabian Peninsula, the Islamic Maghreb, this ISIL group that's been much in the news, and many others. We wake up every morning worrying about it and go to bed every night worrying about it."

"All of us who know history can draw a line from Afghanistan in the 1980s to 9/11," Comey said in 2014. "We are determined not to allow a line from today's Syria to be drawn to future 9/11s. We are determined to anticipate the diaspora of terrorists that's going to happen at some point out of Syria and respond to it aggressively in advance."

Then-Homeland Security Secretary Jeh Johnson bragged in the House Homeland Security Committee on July 14, 2016, that thanks to authority granted by Congress he could deny visa-free travel to citizens of Visa Waiver Program nations who had traveled to seven particular countries.

"With the help of this Congress last year," Johnson said, "we now have the ability to deny visa-free travel to those who have traveled to Syria, Sudan, Iraq, Iran, and -- as a result of the three new countries I added to the list because of this new legislative authority -- Yemen, Somalia and Libya.

But between Comey's June 11, 2014 declaration that the U.S. was "determined not to allow a line from today's Syria to be drawn to future 9/11s" and Obama's departure from office on Jan. 20, 2016, the Obama administration admitted 18,947 refugees from Syria.

It also admitted 34,546 from Iraq and 25,361 from Somalia.

President Trump has ordered the refugee program suspended for 120 days. He has also ordered entry into the United States for most -- but not all -- nationals of the seven countries cited by DHS Secretary Johnson be suspended for 90 days.

During these suspensions, the government will review its screening procedures for allowing travelers into the United States.

Given the testimony Obama's CIA and FBI directors delivered in public hearings, this is a rational and carefully calibrated policy.